Integrated circuit chips are being fabricated with ever smaller geometries and higher circuit densities. The power consumption associated with these increased circuit densities has also increased, thereby increasing the thermal transport requirements of the package. In some conventional thermal transport arrangements, the integrated circuit chip is supported on a metal or ceramic heat spreader. The chip and heat spreader are overmolded by a plastic molding compound which serves as a casing for the package. The thermal impedance of such conventional arrangements has become marginal in view of the increased thermal transport requirements of the higher circuit density packages. This is true even for CMOS technology.
One problem with the conventional arrangement is poor adhesion of the molding compound to the heat spreader surface, particularly with a metal heat spreader. This problem arises because the molding compounds include a mold release agent which permits removal of the molded part from the mold without using an external mold release material. The mold release agent in the molding compound reduces the adhesion between the molding compound and the mold, but also disadvantageously reduces the adhesion between the molding compound and the surface of the metal heat spreader. This poor adhesion often contributes to package cracking due to delamination between the molding compound and the heat spreader.
For example, during conventional surface mounting using reflow soldering, the temperatures (215 C. to 260 C.) produced can enhance the state of thermal mismatch between the molding compound and the heat spreader. The problem is much further aggravated if moisture is present in the molding compound, because the moisture is converted to steam at reflow soldering temperatures. The steam pressure causes more severe delamination and package cracking.
In addition, delamination and cracking as described above can even be caused by temperature excursions within the normal operating temperature of the package.
In view of the foregoing discussion, it is desirable to improve the adhesion between the molding compound and the heat spreader in order to provide increased resistance to delamination and package cracking, while also providing adequate thermal transport capability.
According to the present invention, adhesion between a heat spreader and a substance to be adhered to the heat spreader can be enhanced by using thermal spray deposition to apply a coating to the heat spreader. The substance to be adhered is applied to the coated heat spreader. Such coatings can also be applied to other metal elements within the package to enhance their adhesion capability.